<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    #d1{
      width: 100px;
      height: 100px;
      border: 1px solid red;
      /*设置圆角 值越大越圆 超过宽高的一半为正圆(正方形)*/
      border-radius: 50px;
    }
    #d2{
      width: 100px;
      height: 100px;
      border: 1px solid blue;
      /*默认情况下给元素添加内边距会影响元素的宽高*/
      padding-top: 50px;
      padding-left: 50px;
      /*设置添加内边距不影响宽高*/
      box-sizing: border-box;
    }
    body{margin: 0;}/*去掉body外边距*/
  </style>
</head>
<body>
<div id="d1">边框测试</div>
<div id="d2">内边距</div>
</body>
</html>